Remaining changes to fully support FastDoubleArray.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 9b55ea747545799a7f35aa4948bdcfad46dccd0b..ec9c08352cdfac8ed16c3d58772def333c5010f8 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -2048,6 +2048,7 @@ class FixedArrayBase: public HeapObject {
   static const int kHeaderSize = kLengthOffset + kPointerSize;
 };
 
+class FixedDoubleArray;
 
 // FixedArray describes fixed-sized arrays with element type Object*.
 class FixedArray: public FixedArrayBase {
@@ -2090,6 +2091,10 @@ class FixedArray: public FixedArrayBase {
   // Compute the union of this and other.
   MUST_USE_RESULT MaybeObject* UnionOfKeys(FixedArray* other);
 
+  // Compute the union of this and other.
+  MUST_USE_RESULT MaybeObject* UnionOfDoubleKeys(
+      FixedDoubleArray* other);
+
   // Copy a sub array from the receiver to dest.
   void CopyTo(int pos, FixedArray* dest, int dest_pos, int len);